Hi Wayne,
Many thanks. Believe me I understand the design problem!! I got rid of my
birdie the 'hard way' by removing the loudspeaker circuit from the KPA100's
PCB and hardwiring all the way from the K2's PCB speaker connector to the
speaker, and clipping a ferrite sleeve onto the ribbon cable - I am sure
that you know the type. The receiver's 10m spurious responses in my case
were the 2Fspur = 3Fo - IF and another 3Fspur = 4Fo + IF further down the
band, where Fspur = 32.578 MHz, the bias oscillator's second harmonic
frequency. Both were in the region of 7db above noise floor in a bandwidth
of 1500 Hz, with a dummy load on the antenna input. I have never detected
the 5Fspur = 7Fo - IF potential birdie even in a 200 Hz bandwidth.
I did the removal the 'hard way' to kill all birdies that involved the bias
oscillator in one shot, as other bands were affected.
Again, many thanks.
73,
Geoff
GM4ESD
----- Original Message -----
From: "wayne burdick" <[EMAIL PROTECTED]>
To: "Geoffrey Mackenzie-Kennedy" <[EMAIL PROTECTED]>
Cc: "Elecraft Discussion List" <[email protected]>; <[EMAIL PROTECTED]>
Sent: Saturday, July 16, 2005 6:21 PM
Subject: Re: K2 birdie at 28.265 MHz
The (-) voltage generator (oscillator) in both the KIO2 or KPA100
generates a couple of weak birdies. They will move around a bit from K2 to
K2, because the birdies are the result of high harmonics of this crystal
oscillator mixing with high harmonics of the K2's VCO, and the fundamental
crystal frequency has a tolerance of about +/- 0.5 kHz.
We attempted to position the birdies in obscure parts of the spectrum. If
the 10-meter birdie happens to hit close to a beacon that you want to
monitor (28.265 is in the beacon area of the band), you should be able to
move it a bit by changing one capacitor in the crystal oscillator. In the
KIO2 case, the best choice would be C14. It is normally 56 pF, but
paralleling another 10 pF across it should shift the oscillator a kHz or
two, enough to move the signal off a CW beacon. The value of C14 isn't
critical; it could change +/- 20% without significantly affecting output
of the oscillator.
73,
Wayne
N6KR
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